Obituaries

James Stirling 1953–2018 • John Mulvey 1929–2018 • Paul Baillon 1938–2018

James Stirling 1953–2018

A key figure in the development of QCD

James Stirling

The eminent theoretical physicist James Stirling died on 9 November at his home in Durham, UK, after a short illness. He will be greatly missed, not only by his family but by his many friends and colleagues throughout the particle-physics community. His wide-ranging contributions to the development and application of quantum chromodynamics (QCD) were central in verifying QCD as the correct theory of strong interactions and in computing precise predictions for all types of processes at hadron colliders such as the LHC.

James was born in Belfast, Northern Ireland, and educated at Peterhouse at the University of Cambridge, where he obtained his PhD in 1979. After post-doc positions at the University of Washington in Seattle and at Cambridge, he went to CERN, first as a fellow and then as a staff member, leaving in 1986 for a faculty position at Durham University, where he remained until 2008. At Durham, he played a major role in the foundation of the university’s Institute for Particle Physics Phenomenology in 2000, and served as its first director. He moved to Cambridge in 2008 to take up the Jacksonian Professorship of Natural Philosophy in the Cavendish Laboratory, becoming head of the department of physics in 2011. Then, in 2013, he was appointed to the newly created position of Provost, the chief academic officer, at Imperial College, London, from which he retired last August, moving back to Durham, where his retirement was tragically curtailed by illness.

James was a prolific and meticulous researcher, publishing more than 300 papers, including some of the most highly cited in particle physics. His research, always full of insight, focused on the confrontation of theoretical predictions with experimental results. Over the years, he performed frontier research on a vast range of phenomenological topics. During his graduate studies at Cambridge, in the early days of QCD, he clarified in detail the connection between deep-inelastic lepton–hadron scattering and hadron–hadron processes such as lepton pair production, which led to his later work on parton distribution functions at Durham. An example of his pioneering research is the first computation of the resummed transverse momentum distribution of W and Z bosons in hadron collisions at next-to-leading logarithmic order, performed with Christine Davies in 1984. Another is the development of the powerful helicity amplitude method, completed with Ronald Kleiss while they were at CERN. This enabled them to show that the “monojet” events seen at the CERN proton–antiproton collider, which had been thought to be a possible signal of new physics, could be explained by vector-boson plus jet production. The method has since facilitated the calculation of many other important Standard Model processes.

After moving to Durham in 1986, James formed a long-standing and successful research collaboration with Alan Martin, Dick Roberts and, later, Robert Thorne. Among other projects, they set the standard for determining the quark and gluon distributions in the proton, which led to the widely used MRS, MRST and MSTW parton distribution functions. Later, when James returned to Cambridge, he became interested in processes in which more than one parton from each colliding hadron participates (double parton scattering), bringing a new level of rigour to the analysis of such processes.

James had the gift of being able to explain complicated concepts and ideas simply. He was highly sought after as a plenary or summary speaker at the major international particle-physics conferences. His textbook QCD and Collider Physics, written with Keith Ellis and Bryan Webber, has been a standard reference for more than 20 years.

James was a humble and modest person but his intellectual brilliance, coupled with a very strong work ethic and exceptional organisational skills, meant that his advisory and administrative services were always in great demand. He was elected a Fellow of the Royal Society in 1999, and in 2006 he received the national honour CBE presented by the Queen for his services to science.

In addition to the great respect in which he was held as a scientist, James was much loved as a friend, colleague and mentor. He treated everyone with the same respect, courtesy and attention, whatever their status. His warmth, kindness and fundamental humanity made a deep impression on all who came into contact with him.

Alan Martin Durham University and Bryan Webber University of Cambridge.

 

John Mulvey 1929–2018

Promoting science in all its beauty

John Mulvey

John Mulvey, one of the most enthusiastic supporters of European bubble-chamber physics in its heyday, died on 10 September.

John was brought up in Somerset in the UK, where he decided that he wanted to be a nuclear physicist. He graduated in physics from Bristol University in 1950, and went straight on to study for a PhD, during which he met his wife Denise while supervising her laboratory work as an undergraduate in chemistry. They married in 1955, the year after John submitted his thesis, and in 1956 went together to Los Angeles, where John spent two years as an assistant professor, making many lifelong friends. On their return to the UK, John began his 32 year-long career at the University of Oxford, where he led the Hydrogen Bubble Chamber Particle Physics Group.

John was always dedicated to his work and travelled frequently to help on experiments and attend meetings. In 1971 he took a six-month sabbatical in Hawaii, a memorable experience for the family. For three years, beginning in 1973, John was co-ordinator of the experimental programme at CERN.

An early success at CERN was his participation in the discovery of the K*(1420) resonance at the Proton Synchrotron. Back at Oxford, he set up the precision encoding and pattern recognition project, which measured tracks on bubble-chamber film with an online cathode-ray tube. With his collaborators in Hawaii, he pioneered an experiment at Berkeley to detect transition radiation from electrons passing through foils. His success encouraged Bill Willis to use the technique to detect J/ψ production at the ISR accelerator at CERN. Throughout his career, John encouraged new developments in detectors and accelerator physics at CERN and elsewhere.

During the 1980s he began to take a strong interest in UK science policy. He was frustrated by the cuts to science funding imposed by the Thatcher government and the idea, which was widely discussed, that the government should only fund research that had obvious economic benefits. He became a founding member of the Save British Science (SBS) society and spent much of his time lobbying politicians and businessmen. When he retired from the University of Oxford physics department in 1990, this became a full-time job; he set up an SBS office and ran it for eight years. (Later SBS became CaSE, the Campaign for Science and Engineering, as it is today.) In retirement, John worked on a book that sought to illustrate how research in pursuit of knowledge had frequently resulted in unforeseen benefits.

His life was celebrated at a memorial gathering at Wolfson College in Oxford on 6 October by his family and many friends, colleagues and former students. Speaking for those who had worked with him in particle physics, I recalled how John devoted his life to encouraging and enabling many people from far and wide to engage in unravelling particle science in all its beauty.

Discovery in our science is achieved neither by “prima donnas” working alone nor by groups directed from above, but by people working in dynamic teams held together through mutual respect and confidence – and that is where John made his greatest contribution.

Those who joined the Hydrogen Bubble Chamber Particle Physics Group at Oxford, those who worked with him at CERN, those who joined him to found SBS, and many others, all know how the trust that he engendered cemented international collaborations.

A whole generation of students, who went on to lead great experiments of their own, refer with affection to Uncle John. Indeed, his bright eyes and his smile were still shining when I last visited him.

In the physics department at Oxford there is a room that bears his name – an unusual honour that acknowledges his role in the achievements of the past 60 years and the affection that colleagues, staff and students had for him.

Wade Allison Keble College, University of Oxford.

 

Paul Baillon 1938–2018

Passion across disciplines

Paul Baillon

Paul Baillon, who was notable for the sheer variety of his output in particle physics and astrophysics, passed away on 2 October at the age of 80.

Paul was a pioneer in bubble- chamber physics. A graduate of École Normale Supérieure, he joined the École Polytechnique laboratory for his PhD. In 1961 and 1962 he participated in an experiment that recorded 750,000 antiproton annihilations at rest in liquid hydrogen at the 81 cm Saclay Bubble Chamber. His thesis, completed in 1965, presented a new determination of the mass and width of the K meson and described new resonances, in particular the first pseudoscalar meson in the 1400–1500 MeV mass region. Paul kept an interest in this subject because the meson could be interpreted as being made up of gluons (a “glueball”), and, 20 years after the data was recorded, he even carried out a new analysis looking for baryonium states.

In 1966 Paul became a CERN staff member. From 1974 to 1982, he took part in experiments at the Proton Synchrotron that focused on the study of two-body hadronic reactions, and then spent a period of time at SLAC in the US, where he participated in the DELCO experiment at the PEP electron–positron collider, studying in particular the charm quark and the tau lepton.

Throughout his career, in parallel with his work at CERN, Paul managed to continue to collaborate with his French colleagues, often in his spare time. He was passionate about astrophysics and was one of the originators of gamma-ray astronomy in France through his involvement in the Themistocle experiment, carried out from 1988 to 1994. Later, he participated in the design of the CAT (Cherenkov Array at Themis) gamma-ray imaging telescope.

Paul was also involved in searches for dark matter based on the gravitational microlensing of background stars, contributing to the AGAPE and POINT-AGAPE searches conducted at the Pic du Midi and Las Palmas obser­vatories in France and the Canary Islands.

Upon his return from the US, Paul again joined CERN’s particle-physics programmes – first LEP and the DELPHI experiment, where he helped design and build the complex and innovative RICH Cherenkov detector. He then joined the CMS experiment at the LHC and made essential contributions to the design of the scintillating-crystal electromagnetic calorimeter, in particular the system that stabilises the crystal temperature to within a few hundredths of a degree.

With a solid foundation in classical physics and instrumentation, as well as in mathematics, Paul was as passionate about the construction of a detector as he was about abstract ideas in mathematical physics. Many still remember, for example, his highly informative class on the use of tensor calculus at the Herceg Novi school in 1968. In his retirement, he wrote a book entitled: Differential Manifolds, A Basic Approach for Experimental Physicists. He was writing a second on the basics of quantum field theory.

When faced with a problem, Paul had the knack of approaching it from an unexpected angle. It was a sign of brilliance, of true originality and even of a certain taste for the paradoxical, but it always produced results. Gifted and daring in his intellectual pursuits, he was also an accomplished skier and mountaineer. Beyond science and sport, Paul was interested in history and religion, and found time to get involved in politics and local affairs.

We will treasure the memories of our discussions with Paul, an exceptional scientist and person.

His colleagues and friends at CERN and beyond.